The overall objective of this proposed research is to develop near-infrared (NIR) imaging methods for the detection and diagnosis of early dental caries (dental decay). New, more sophisticated diagnostic tools are needed for the detection and characterization of caries lesions in the early stages of development. If carious lesions are detected early enough, before cavitation, then they can be arrested/remineralized by non-surgical means through fluoride therapy, anti-bacterial therapy, dietary changes, or by low intensity laser irradiation. It is not sufficient to simply detect caries lesions, methods are needd to assess the activity of the lesion and determine if chemical intervention is needed. Previous in vitro and in vivo studies have demonstrated that optical coherence tomography can be used to nondestructively image the subsurface lesion structure and measure the thickness of the highly mineralized surface zone. Other studies have demonstrated that the rate of dehydration can be correlated with the lesion activity and that rate can be measured using optical methods. The central hypothesis underlying this proposal is that there are structural differences between active lesions due to caries, arrested lesions and developmental defects, and these differences can be resolved nondestructively using optical imaging methods at NIR wavelengths. Arrested lesions and developmental defects of enamel can be easily mistaken for active early caries lesions due to similar texture and color. Arrested lesions and mild developmental defects typically have a hard outer layer or surface zone of higher mineral content than the body of the lesion which reduces the lesion permeability. The overall objectives of this proposal will be achieved through the following specific aims: (1) To test the hypothesis that optical methods can be used to assess lesion activity on tooth coronal and root surfaces, (2) To test the hypothesis that NIR imaging methods can be used to differentiate caries lesions on tooth coronal surfaces from enamel hypomineralization due to developmental defects. It is likely that if these studies and future clinical trials are a success, this novel imaging technology will be employed for the detection and monitoring of early carious lesions without the use of ionizing radiation, thereby enabling conservative non-surgical intervention and the preservation of healthy tissue structure.